The present invention relates to a safety valve for preventing gas pressure from increasing beyond an acceptable level and to an electromagnetic valve that serves as the safety valve.
Conventionally, high-pressure gas supply systems such as gas tanks for fuel-cell cars have valve devices. An electromagnetic valve is known as one example of such a valve device and is used for controlling supply of hydrogen gas stored in the gas tank mounted on a fuel-cell car (for example, refer to Japanese Laid-Open Patent Publication No. 2003-240148). Such valve devices function, for example, as safety valves that prevent gas pressure from increasing beyond an acceptable level, that is, such valve devices prevent excessive pressure from being generated.
The internal pressure of the gas tank for a fuel-cell car, that is, the pressure of hydrogen gas stored in the gas tank, is as high as, for example, 70 MPa. Charging of hydrogen gas into a gas tank is performed, in some cases, by using a charging device that uses a pressure reducing valve for lowering a charging gas pressure, which is higher than the tank internal pressure and is, for example, approximately 200 MPa.
However, if the pressure reducing valve of the charging device malfunctions and the charging gas pressure is applied to the gas tank without being lowered, the internal pressure of the gas tank can be instantly increased beyond the acceptable level. In such a case, hydrogen gas in the gas tank (and in the high-pressure gas passage) is discharged to the outside by a safety valve. This prevents the gas pressure from increasing beyond the acceptable level.
Specific examples of such safety devices include those disclosed in Japanese Laid-Open Patent Publications No. 11-182722 and No. 59-197680, which disclose configurations using a breakable member such as a rupture disc. Such a disc is ruptured when the pressure in a high-pressure gas passage is increased, to discharge gas in the high-pressure gas passage to the outside. Also, as disclosed in Japanese Laid-Open Patent Publication No. 11-151160, a relief valve using spring force can be used as a safety valve for high-pressure gas.
However, the limit pressure, at which the breakable member is ruptured, that is, the rupture limit of the breakable member is difficult to control. Thus, reduction in costs through mass production of breakable members cannot be expected. Also, a relief valve that utilizes spring force has the drawback that it is larger in size than the breakable member. In addition, particularly in a hydrogen gas supply system, embrittlement of the spring can hamper the operation of the relief valve. Therefore, there is a demand for a simple, inexpensive and accurate safety valve.